224 GENERAL CHARACTERISTICS. 



arguments, and sought for a remedy. This he found in the so-called 

 dilution method, by the aid of which, in 1877, he produced from 

 sour milk a pure culture of a fission fungus to which he applied 

 the name of Bacterium ladis as before this time correctly. The 

 twofold origin of this name should therefore always be remembered. 

 Lister was also the first to make the observation, subsequently 

 confirmed by Cohn, that lactic acid bacteria, though of frequent 

 occurrence in the rooms of dairies, are comparatively seldom found 

 in the open air. 



The introduction of gelatinised nutrient media into bacteriology 

 also furthered the study of lactic fermentation. By means of this 

 new method of pure cultivation HUEPPE (IV.) in 1884 isolated 

 from sour milk a microbe known as Bacillus acidi lactici, which, 

 in so far as can be gathered from the description given, was 

 identical with Lister's bacterium. Hueppe also made the more 

 important discovery that several different species of bacteria are 

 capable of setting up lactic fermentation. However, before 

 noticing these other organisms, we will examine more closely the 

 Bacillus acidi lactici, which occurs in the form of non-motile rods 

 1.0-1.7 /* l n o an d 0.3-0.4 [j, broad, mostly in pairs and but rarely 

 united to form a four-cell chain ; it is aerobic and forms endospores. 

 This ferment acidifies milk between the temperatures of 10 and 

 40 C., the reaction being accompanied by the precipitation of 

 casein, and an evolution of gas. On gelatin plates the organism 

 forms white colonies which do not liquefy the nutrient medium. 



In addition to the five species of lactic acid bacteria discovered 

 by Hueppe and to which Micrococcus prodigiosus belongs many 

 others possessed of the same property have been made known to us, 

 by Maddox in England (1885), Beyer in North America (1886), 

 and FOKKER (II.) in Holland (1890). R. KRUEGER (I.) isolated 

 his Micrococcus acidi lactis (which liquefies gelatin) from cheesy 

 butter. G. MARPMANN (I.) discovered five species belonging to this 

 group in Gottingen milk, and named them Bacterium lactis acidi, 

 Bacillus lactis acidi, Bacterium limbatum lactis acidi, Micrococcus 

 lactis acidi, and Sphcerococcus lactis acidi. G. GROTENFELT (II.) 

 isolated a lactic-acid-forming, anaerobic Streptococcus acidi lactici 

 from Finnish milk. In his communication, issued from Hueppe's 

 laboratory, there also occurs the remark that Bacillus acidi lactici H. 

 can be permanently deprived of its acidifying power by cultivating 

 it for some time in media free from sugar. This attenuation of the 

 cultures is also often noticed in pathogenic bacteria, many of which 

 lose their virulence i.e. poisonous nature and consequent capacity 

 of producing disease when kept for some time under unaccus- 

 tomed conditions of nutrition, viz., outside the animal body. 

 Bearing this in mind, Grotenfelt speaks of a variable virulence 

 of Bacillus acidi lactici, meaning thereby the possibility of re- 

 ducing its fermentative power. 



The fermentative properties of the Bacterium lactis aerogenes, 



